This invention relates to a method for positioning seamed balls, and more particularly to a method for automatically positioning the seamed balls such as known tennis balls, baseballs and the like, each having a known curved endless seam line which divides an entire ball surface into a pair of identical, dumbbell-like parts, hereinafter referred to as "dumbbell sheet(s)" or "dumbbell(s)", each of which has a pair of identical round hip portions joined by a waist portion which is most reduced at its middle portion.
The term "seamed ball(s)" herein used includes not only such balls as having a real seam line along which the pair of dumbbell sheets are actually joined together but also such balls as having a false seam line formed, for example, by molding, printing, painting or any other process.
In manufacture of the seamed balls each having the above mentioned endless seam line appearing on the external spherical surface thereof, it is necessary to make each of the seamed balls correctly positioned so that a certain predetermined face thereof is directed toward a certain predetermined direction, in order that, as shown in FIG. 1A, a certain commercial indication ID such as a trademark is properly stamped or printed on a constant surface spot of each ball SB, for example on the central surface spot of a waist portion W of one of the dumbbells.
Such ball positioning is also necessary when inspection of compressibility of the seamed balls SB is performed. For example, J. T. A. Standard (the standard of Japan Tennis Association) prescribes that the inspection of compressibility should be carried out by applying a certain compressive pressure onto a central surface spot C1 (hereinafter referred to as "hip center") of one of the hip portions H of the dumbbell as shown in FIG. 1B or a central surface spot C2 (hereinafter referred to as "waist center") of the waist portion W of the dumbbell as shown in FIG. 1C.
Therefore, there exists a strong demand for a method for an apparatus which enables the automatic positioning of the seamed balls. In fact, however, no satisfactory technique therefor is available at present. Although an attempt to utilize a known image sensor to realize such automatic ball positioning was once proposed, it turned unsuccessful because of unsatisfactory accuracy, inefficiency and a high cost.
Therefore, the fact is that the ball positioning is now carried out by manual operation in many factories producing the seamed balls. However, such manual operation is apparently inefficient, labor-consuming, and unsatisfactory in accuracy.
It is, therefore, an object of the present invention to solve the above discussed problems in positioning the seamed balls such as tennis balls.
Another object of the invention is to provide a method which enables the automatic positioning of the seamed balls.
A further object of the invention is to provide a method for automatically locating the hip center of each seamed ball on a certain imaginary axis which extends through the center of the ball, in a process for stamping or printing a certain commercial indication to a predetermined spherical surface spot of each seamed ball or in a process for measuring a compressibility of the produced seamed balls for inspection purposes.
A still further object of the invention is to provide a method for automatically locating the waist center of each seamed ball on a certain imaginary axis which extends through the center of the ball, in a process for stamping or printing a desired commercial indication at a predetermined spherical surface spot of the ball or in a process for measuring a compressibility of the produced seamed balls for inspection purposes.
The above and other objects, features and advantages of the invention will become apparent from the following description of preferred embodiments thereof taken in connection with the accompanying drawings.
According to the present invention, there is provided a method for positioning seamed balls each having an endless curved seam line which divides a whole spherical surface of the ball into a pair of identical dumbbell-like parts each having a predetermined maximum longitudinal length F and a predetermined minimum crosswise length D, the sum of such lengths F, D being equal to an entire circumference of the ball, wherein each of the dumbbell-like parts has a pair of identical round hip portions joined by a waist portion which is most reduced at its middle portion, and each of the hip portions is defined by a part of the seam line which is an arc of a spherical circle with a predetermined radius which is equal to a distance from the arc to a center of the spherical circle referred to as a hip center, which comprises steps of:
(a) supporting each of the balls so that its center is located at the origin of a three-dimensional orthogonal coordinate system consisting of two horizontal axes X, Y and one vertical axis Z;
(b) rotating the ball on the axis X (and/or Y) until an optical sensor disposed on the axis Z can specify such a particular locus that is constituted by successive points of intersection of the axis Z and the spherical surface of the ball and that intersects the seam line at four points during one full rotation of the ball thereby to provide four arcs along the locus;
(c) finding the shortest arc among the four arcs on the locus by means of the sensor and then rotating the ball on the axis X (or Y) that is perpendicular to a plane including the locus, to locate a mid point of a length of the shortest arc on the axis Z by the aid of the sensor;
(d) rotating the ball on the axis Y (or X) that extends in the plane which includes a chord subtending the shortest arc until an intersection of a bisector perpendicular to the chord and a part of the seam line subtended by the chord is located on the axis Z by the aid of the sensor;
(e) rotating the ball on the axis Y (or X) by an angle of 360R/D+F or 360(F-R)/D+F in one direction or 360(R+D)/D+F in the opposite direction; and
(f) stopping rotation of the ball upon locating the hip center on the axis Z so that an imaginary polar axis of the ball defined by an imaginary line extending through an opposed pair of the hip center is located on the axis Z.
The invention includes a further aspect wherein the hip center thus determined is utilized to determine a waist center, whereby each of the seamed balls takes its constant position.